Biology · Enzymes

All of the water-soluble vitamins and two of the fat-soluble vitamins, A and K, function as cofactors or coenzymes. 

Option (a) refers to a group of vitamins collectively known as vitamin B complex. Vitamin B complex consists of several B vitamins, some of which act as coenzymes. However, "Vitamin B" is a broad term and does not specify a single vitamin. 

Option (b) refers to thiamine, which is also known as Vitamin B1. Thiamine acts as a coenzyme in several metabolic reactions, particularly in carbohydrate metabolism, helping to convert food into energy. 

Option (c) refers to riboflavin, which is also known as Vitamin B2. Riboflavin serves as a precursor for coenzymes like flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN), which are involved in various cellular reactions, including energy production. 

Option (d) suggests that all the listed vitamins (Vitamin B, Vitamin B1, and Vitamin B2) act as coenzymes. While some B vitamins act as coenzymes, it is not accurate to say that all vitamins within the B complex function as coenzymes.